The present invention refers to radio frequency signal receivers and, in particular, to a transistor mixer and amplifier input stage for such a receiver, which is adaptable to being implemented by an integrated circuit.
The dynamic range of a receiver input stage, i.e. the difference between the maximum and minimum input signal level that can be accepted without introducing appreciable distortion, is limited on the low side by the stage sensitivity, and limited on the high side by the finite range of linearity of the transfer characteristic of the stage itself.
To modify the input circuit stage in a simple way in order to increase its input dynamic range, various techniques have been explored, one of which is mentioned later in this text, and which makes possible a more linear stage response. Nevertheless, in each of such cases, the techniques result in the deterioration of other parameters, such as sensitivity, the passband, and the maximum gain; consequently, the signal to noise ratio for low input signal levels is deteriorated. It is also possible to resort to more elaborate techniques, as are described, for example, in the article entitled "AM-FM Car Radio for Tomorrow" by R. Graziadei and G. Seragnoli, published by IEEE Transactions on Consumer Electronics, Vol. CE-26, August 1980, pp. 271-281. These techniques however, require rather complex circuits which are relatively critical in their component values.